Powder metal ultrasonic welding tool and method of manufacture thereof

ABSTRACT

An ultrasonic welding tool fabricated of powder metal material includes a body and a welding tip extending axially from the body to a working end. The powder metal material can be ferrous-based and admixed with additives, such as alumina, carbide, ferro-molybdenum, ferro-nickel, chrome or tribaloy. An exposed surface of the welding tip can comprise Fe 3 O 4  oxides. The tool is compacted to the desired shape and sintered. The body can include a different second material compacted separately from the welding tip and then joined to the tip and sintered.

CROSS-REFERENCE TO RELATED APPLICATION

This divisional application claims the benefit of U.S. ProvisionalApplication Ser. No. 60/802,753, filed May 23, 2006, and U.S. Utilityapplication Ser. No. 11/689,675, filed Mar. 22, 2007, and U.S. C-I-Papplication Ser. No. 12/435,261, filed May 4, 2009, and U.S.Continuation application Ser. No. 13/476,184, filed May 21, 2012, whichare incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention relates generally to ultrasonic welding tools, and moreparticularly to the materials and process used to make such tools.

2. Related Art

Ultrasonic welding is a technique used to join parts or workpiecescomprising hard and soft plastics, and metals. In ultrasonic welding ofthermoplastics, vibratory energy is applied to the plastic workpieces byan ultrasonic welding tool, causing local melting of the plastic. Thevibrations are transferred through the plastic workpieces to the jointto be welded. The tool can remain in a single location on one of theworkpieces to be welded and the ultrasonic energy will travel throughthe plastic workpieces and weld the entire joint.

Ultrasonic welding can also be used to join metals, preferablydissimilar metals. The vibrations travel through the metal workpiecesand the welding occurs due to local motion of the metal material andhigh-pressure dispersion of surface oxides. The high frequencyvibrations cause some heating of the metals, but not enough to melt themetals.

Ultrasonic welding can also be used to enhance the soldering process.Ultrasonic soldering includes introducing the high frequency vibrationsinto molten solder and introducing a cavitation action at the weldingtip, which disrupts and disperses the surface oxides. The disruption ofthe surface oxides permits the solder to wet the metal workpiece so thata solidified solder is formed behind the tool.

Ultrasonic welding is a preferred method of joining small workpieceswhich are too delicate for traditional welding techniques, such as wiresand delicate circuits. Ultrasonic welding is widely used in thepackaging industry, especially for foods and medical supplies. Further,ultrasonic welding is quicker than traditional welding systems, and itdoes not require a ventilation system to remove heat or exhaust, whichare often needed in other welding systems.

An ultrasonic welding system typically includes a power supplydelivering a high power AC signal to a converter, which converts the ACsignal into a mechanical vibration. As indicated above, the ultrasonicwelding tool, also known as a sonotrode or horn, applies the highfrequency vibrations to the workpieces to be welded. A booster can beused to modify the amplitude of the vibration. The converter, booster,and tool are specifically tuned to resonate at the same ultrasonicfrequency, which typically ranges from 15 kHz to 70 kHz. The workpiecesto be welded are held in a press under pressure to prevent theworkpieces from being forced apart as the tool applies the mechanicalvibrations.

Although ultrasonic welding has numerous advantages, the technique haslimited use due inadequacies of the tool. Existing ultrasonic weldingtools are typically wrought or cast from a metal alloy. Upon forming thebasic structure of the tool, it must be machined to achieve desiredfeatures and shape, which is costly and complex. The manufacturing andfinishing processes limit the selection of material available for use asan ultrasonic welding tool. Further, the available materials are notcompatible with the workpieces to be joined, thus further limiting theuse of ultrasonic welding as a method of welding workpieces.

SUMMARY OF THE INVENTION AND ADVANTAGES

The ultrasonic welding tool includes a welding tip fabricated of powdermetal material for applying a high frequency vibration to at least twoworkpieces to be welded. The tool is compatible with a wide range ofmetallic workpiece materials.

A method of fabricating the ultrasonic welding tool includes compactinga powder metal material and sintering the powder metal material at aboutambient pressure which is not under a vacuum. The method canalternatively include compacting a first powder material to form awelding tip and compacting a second powder material to form a body ofthe ultrasonic welding tool separately from the welding tip. The weldingtip and the body are joined and sintered.

The use of a powder metal material allows a great range of materials tobe used in the tool. For example, the invention contemplates the use ofmetal alloys, blends and admixtures of metals, high wear compositematerials, and high friction composite materials such as cermets.Further, powder metal material comprises an inherently porous structureso that additives can be used in the powder metal mix to adjust thestrength and other physical characteristics. The powder metal materialcan also be treated to adjust the physical characteristics of the tool.The powder metal mixture, additives, and treatments can be selected tobest suit the workpieces to be welded, so that the tool is compatiblewith more workpieces to be welded. Further, the mixture, additives, andtreatments can be adjusted to meet cost restraints.

The powder metallurgy process will enable the formation of a gradientstructure in either materials and/or properties of the tool. Forexample, the welding tip can comprise a very hard and more costly powdermetal composition, while the body can comprise a lower-cost material.The powder metallurgy process enables the tool be made near net shapewithout extensive post fabrication machining or finishing operations.Further, different portions of the tool can be formed independent of oneanother so that they can be selectively designed to achieve desiredphysical characteristics and then subsequently joined to one anotherduring sintering.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other advantages and features of the present invention willbecome more readily appreciated when considered in connection with thefollowing detailed description and drawings, in which:

FIG. 1 is a schematic perspective view illustrating the components of anultrasonic welding system;

FIG. 2 is an enlarged fragmentary perspective view of a welding tip ofan ultrasonic welding tool;

FIG. 3 is a further enlarged fragmentary perspective view of a weldingtip end of an ultrasonic welding tool; and

FIGS. 4 through 8 are cross-sectional views illustrating differentembodiments of ultrasonic welding tools constructed according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

Figure I illustrates a typically ultrasonic welding system including apower supply 20, converter 22, booster 24, press 26, and an ultrasonicwelding tool 28 according to the invention. The ultrasonic welding toolis generally shown at 28 and comprises a body 30 and a welding tip 32 orprobe extending axially from the body 30 to a working end 34 forapplying a high frequency vibration to a workpiece 36 to be welded. Theworking end 34 includes a face 38 serving as the functional surface incontact with a workpiece 36 to effect the formation of an ultrasonicweld between two workpieces 36.

The ultrasonic welding tool 28 can take on any of a number of shapes andfeatures. FIG. 2 illustrates one embodiment of the tool 28 wherein thebody is generally cylindrical, and the welding tip 32 can be providedwith flats 40. The present invention is not limited to any particularshape and/or size of the welding tip 32, nor are there limits to thenumber and shape of various surfaces of the welding tip 32. Further, thebody 30 can present a shoulder region 46 providing a shoulder surface 42from which the welding tip 32 extends, as shown in FIGS. 1-8. Theshoulder region 46 is not limited to any particular size and/or shape,for example the shoulder surface 42 can have an angled, cupped, orconcave configuration. FIGS. 3 and 4 illustrate another embodiment ofthe tool wherein the shoulder surface 42 comprises a contoured profiledextending into the welding tip 32. The overall configuration of theultrasonic welding tool 28 is not limited to the disclosed embodiments,which are meant to be exemplary, and contemplates any ultrasonic weldingtool 28 configuration suitable for ultrasonic welding that may bepresently available or developed in the future.

Turning now to particular aspects contemplated by the present invention,at least the welding tip 32 of the ultrasonic welding tool 28 isfabricated of a powder metal material which has been compacted andsintered to the desired shape. One advantage of powder metallurgy isthat it enables the ultrasonic welding tool 28 to be made near net shapeto the desired final tool 28 configuration without extensive postfabrication machining or secondary finishing operations of the tool 28.Another advantage is that it enables a wide selection of materials thatmight not otherwise be available for use in connection with wroughtultrasonic welding tools.

In one example of FIG. 4, the entire ultrasonic welding tool 28 isfabricated of the same powder metal material. For example, the tool 28may be fabricated of an iron based pre-alloyed powder metal material,such as M2 or H13 tool steels. These materials are compacted and thensintered to near net shape and may be used with little post-formingfinishing of the tools.

Powder metal material is advantageous in connection with ultrasonicwelding tools 28 in that the inherent porous structure of the materialincreases the friction coefficient as compared to a wrought material.The use of powder metal also reduces the thermal conductivity ascompared to wrought tools. This acts to maintain more heat at the tool28 and workpiece 36 interface since the powder metal tool 28 has less ofa heat sink effect than that of a wrought tool counterpart. The basematerial may further be treated or altered to vary the properties,including altering the coefficient of friction and/or the wearresistance. For example, as shown in FIG. 4, an exposed surface 44 ofthe welding tip 32 may be steam treated under high temperature andpressure to effectively oxidize and convert the exposed surface 44 ofthe welding tip 32 to Fe₃O₄, which is a highly stable form of ironoxide, that has the effect of increasing the wear resistance andfriction coefficient of the iron-based powder metal material.

Friction-altering powder additives can be admixed with the powder metalmix to improve the working properties of the tool 28. The additives mayincrease or decrease the kinetic coefficient of friction of theultrasonic welding tool 28 to respectively increase or decrease the heatgenerated during use of the ultrasonic welding tool 28. Accordingly, thetool 28 can be selectively manufactured to generate the desired amountof heat in use, thereby reducing workpiece-to-tool adhesion, whileproviding the desired weld properties, depending on the materialproperties of the workpieces 36 be joined. The additives can be added tothe powder metal mix prior to compaction, and then pressed and sinteredin-situ. For example, additions CaF₂, MnS, MoS₂, BN, CaCO₃, silica,alumina, ceramic, carbide compounds, and other hard, stable particles,such as ferro-molybdenum, ferro-nickel, chromium and/or tribaloy, may beadded to improve the working performance of the base powder metalmaterial. The invention is not limited to any particular composition ofmaterial and, within its scope, is directed to the broad concept ofusing powder metallurgy to form ultrasonic welding tools 28 withoutregard to any particular composition.

Post sinter processing may also include resin impregnation or otherimpregnation material to fill the porosity of at least certain portionsof the tool 28 to enhance the working performance of the tool 28. Theimpregnation can include various materials which, as mentioned, willalter the kinetic coefficient of friction of the tool 28, the thermalconductivity, and working performance of the tool 28. This includes theinfiltration of a material having a lower melting point than the basepowder metal mix to fill the porosity of the powder metal material. Onecommon infiltration technique uses Copper base alloys.

The use of powder metallurgy also enables the maker of the tool 28 toalter the properties, as desired, in different regions of the tool 28.This can be done via the sintering process alone and/or through the useof mixtures of various powders, alloys, and additives to provide ahybrid of microstructures including a variety of microstructural phasegradients throughout the tool 28. For example, a combination of hardphase, soft phase and carbide precipitates in the microstructure mayprovide strength, ductility and wear resistance properties not availablein a single phase structure. The various phases and features may includeferrite, pearlite, bainite, martensite, metal carbides, hypereutectoidand hypoeutectoid phases and various precipitates, for example.

In addition, sintering aid additives, which are added to the powdermetal mix prior to compaction, can be used to facilitate manufacture ofthe tool 28. The sintering aid additives can improve the strength andother properties of the tool 28, such as wear resistance, and thermalproperties, for example, through liquid phase, transient liquid phase orenhanced solid solution mechanisms. Some examples of sintering aidmaterials include, by way of example and without limitation, MoS₂,phosphorous and phosphorous compounds, boron, cobalt, tin, and othermaterials that improve the degree of sinter and/or density of thecompacted region of the tool 28.

As mentioned, different process treatments can be used on selectedregions of the ultrasonic welding tool 28, thereby altering thecomposition of the material in different regions. Accordingly, as shownin FIG. 5, for example, the welding tip 32 is made of one material whichmay have properties of extremely good wear resistance and high hardnessin order to best function and withstand the pressures and temperaturesassociated with the welding tip 32 as it contacts and applies the highfrequency vibrations to the workpieces 36 to be welded, and the body 30can be made of a different second material if desired which mayconstitute a lower alloy, less expensive material. Further, the shoulderregion 46 can be fabricated of yet another different material exhibitinggood wear resistance but also exhibiting a high friction coefficient tomaximize the welding capabilities of the tool 28 during ultrasonicwelding.

FIG. 6 is a variation on FIG. 5 in which the welding tip 32 and shoulderregion 46 of the tool 28 are fabricated of one powder metal material,whereas the remaining portions of the body 30 are fabricated of a secondpowder metal composition. Of course, the welding tip 32 could befabricated of powder metal to achieve the advantages described hereinwhich may be cemented or otherwise joined to a body 30 made of adifferent second material, which may not necessarily be a powder metal,in order to reduce costs or offer an alternative to an all-powder metalultrasonic tool 28 if desired.

FIG. 7 illustrates another gradient powder metal structure of theultrasonic welding tool 28, in which a core 48 of the tool 28 may befabricated of one material, such as a high load, high wear resistancematerial, and an outer layer 50 or sheath of the tool 28, is fabricatedof a second material which may be a wear resistant, but highercoefficient of friction material than that used for the core 48.

Finally, FIG. 8 illustrates another friction stir welding tool 28, inwhich various portions of the tool 28 are constructed separately fromone another, and thereafter sinter bonded to one another. As such, thewelding tip 32 can be compacted from one powder mixture, the shoulderregion 46 from another powder mixture, and the remaining portions of thebody 30 from yet another powder mixture. Thereafter, the separateportions are sintered together. Sintering additives or other additivescan also be incorporated in one or more of the powder mixtures of therespective portions, as desired. It should be recognized that the numberof portions constructed separately from one another can be varied, asnecessary, to obtain the tool 28 structure desired.

Another aspect of the invention includes a method of manufacturing atool 28 in accordance with the embodiments above. The method includescompacting a powder metal material and sintering the powder metalmaterial at or about ambient pressure which is not under a vacuum or ina closed chamber pressure vessel. This method is used to form thewelding tip 32 of the tool 28 having the working end 34. The method caninclude forming the other portions of the respective tool 28, andjoining the portions to one another. One aspect of the manufacturingprocess contemplates that the sintering can be conducted in acontinuous-style furnace at temperatures above 900 degrees C.

Where adjacent ones of the respective portions, and, including theirvarious embodiments, are compacted from powder, the method furtherincludes joining the separate portions to one another by a diffusionprocess within a sintering furnace. Sintering enhancement additives orother techniques can be used in the sintering process. It should berecognized that various combinations of the aforementioned body 30,shoulder region 46, and welding tip 32 may be constructed as one pieceor separately from one another, and joined together via the sinteringprocess.

It is to be understood that other embodiments of the invention whichaccomplish the same function are incorporated herein within the scope ofany ultimately allowed patent claims.

1. A method of manufacturing an ultrasonic welding tool comprising apowder metal material including the steps of: compacting a ferrous-basedpowder metal material to form a welding tip; sintering the powder metalmaterial at about ambient pressure which is not under a vacuum; andforming Fe₃O₄ in the welding tip.
 2. A method as set forth in claim 1wherein said sintering is further defined as sintering in acontinuous-style furnace.
 3. A method as set forth in claim 1 furthercomprising including at least one additive in the powder metal material,wherein the at least one additive is selected from the group consistingof CaF₂, MnS, MoS₂, BN, CaCO₃, SiO₂, Al₂O₃, ferro-nickel, and an alloyof Cr, Ni, and Co.
 4. A method as set forth in claim 1 wherein the stepof forming the Fe₃O₄ comprises steam treating the powder material tooxidize and convert an exposed surface of the ultrasonic welding tool toFe₃O₄.
 5. A method as set forth in claim 1 further comprisingimpregnating a resin in pores of the powder metal material.
 6. A methodas set forth in claim 1 further comprising infiltrating copper in poresof the powder metal material.
 7. A method as set forth in claim 1further comprising: compacting a second material to form a body of theultrasonic welding tool separately from the welding tip; and joining andsintering the welding tip and the body.